protobuf 3.11+ does not compile with GCC 4.8.5 available from stock
RHEL/CentOS 7 packages.  RHEL/CentOS 6 faced a similar issue after
protobuf version was bumped to 3.6 and the solution was to use
devtoolset-7 on that operating system.  Since devtoolset-8 is the latest
C toolchain SCL available for both RHEL/CentOS 6 and RHEL/CentOS 7, use
it for building protobuf on those operating systems.